As semiconductor devices become more highly integrated and have increasingly high performance, a FinFET transistor having a three dimensional structure has been suggested. A FinFET is a non-planar, double-gate transistor built on a SOI substrate. A distinguishing characteristics of the FinFET is that the conducting channel is wrapped by a thin silicon “fin,” which forms the gate of the device. The thickness of the fin determines the effective channel length of the device.
A FinFET transistor can be formed having a gate electrode with a high aspect ratio. Also, to embody a high performance transistor, a metal gate electrode is used instead of polysilicon, which can be formed by a Damascene method. To this end, a sacrificial layer having the same shape as the metal gate electrode is formed. Accordingly, the sacrificial layer is also to have a high aspect ratio. However, since the thickness of a gate insulation layer decreases for high integration, the sacrificial layer is etched at a fast etch speed, that is, a high etch selectivity with respect to an insulation layer. However, since a fast etch speed makes the sacrificial layer have a taper shape in which a lower side is wider than an upper side, undesired voids are generated in a subsequent process of forming a metal gate electrode. Furthermore, reliability of a device may be deteriorated.